1. Field of the Invention
The present invention relates to a static random access memory (SRAM) device, more particularly, to a static random access memory device using melt-recrystallization technology and silicon on insulator (SOI) technology.
2. Description of the Related Art
Conventionally, a SRAM is used for maintaining data by a battery back up, and a memory cell for the SRAM is preferably used for a full CMOS configuration to decrease a power consumption thereof. Namely, the memory cell for the SRAM is constituted by two CMOS inverters and two switching transistors. For example, the switching transistors are constituted by N-channel type MOS (or MIS: Metal Insulator Semiconductor) transistors, and each of the CMOS inverters is constituted by a P-channel type MOS transistor and an N-channel type MOS transistor.
Note, six transistors of the memory cell for the SRAM are practically formed as a three-dimensional configuration to increase an integration thereof by using SOI technology. Namely, in this memory cell, four N-channel type MOS transistors are formed on a substrate (lower layer), an interlayer insulation film is formed on the N-channel type MOS transistors, and two P-channel type MOS transistors are formed on a melt-recrystallization silicon layer (upper layer) which is formed on the interlayer insulation film, or above the lower layer. Further, the P-channel type MOS transistors formed on the upper layer are connected to the N-channel type MOS transistors formed on the lower layer through contact holes formed in the interlayer insulation film by aluminium wiring.
For example, in the memory cell for the SRAM according to the prior art, a gate of a P-channel type MOS transistor formed on the upper layer of a first CMOS inverter is connected to a drain region of an N-channel type switching MOS transistor, and a gate of an N-channel type MOS transistor is formed on the lower layer of a second CMOS inverter by filling aluminium into a contact hole above the drain region of the switching transistor. Therefore, an aspect ratio of the contact hole becomes large and a coverage of the aluminium wiring becomes bad, and thus the aluminium wiring may be snapped.